Glasgow, Scotland (CNN) - Robert Marshall is the burly, landlord of The Louden Tavern, a pub located in the west end of the Scottish city of Glasgow, on the south bank of the same Clyde River that was once used to ferry coal and steel to the great shipbuilding companies that in the past made this area an industrial powerhouse.

There is no doubt as to which soccer team Marshall and his clientele give their loyalties. Decorated in the team colors of red, white and blue throughout its interior and situated only a stone's throw from the famous Ibrox Stadium, the bar is overt in its homage to Rangers Football Club.

Its position around the corner from the Glasgow Orange Order - a Protestant fraternity who still march once a year to celebrate the victory of King William III over the Catholic King James II in 1690 at the Battle of the Boyne - may be a mere coincidence, the allegiance of its regulars to Rangers is not.

Across town, on the Gallowgate road, Tommy Carberry pulls pints in Bairds Bar, a building daubed in the green hue synonymous with Celtic Football Club. The pub sits a mile-or-so from Celtic Park - the 60,000-seater home ground of the 42-time Scottish title winners - and is a much-loved stopping point for fans attending the match.

Celtic wears its Irish and Catholic heritage very much on its sleeve - or chest to be more exact, as the club's four-leafed clover badge sits on the left breast of its players - which is maybe not surprising for a team founded by a member of a Catholic religious order in 1888.

The two landlords - who remarkably, are childhood friends - represent two of Glasgow's communities in a microcosm, one passionately British and Protestant, the other proud of their Catholic and Irish heritage, a division which mirrors the sectarian lines of Northern Ireland, loyalties forged over centuries of war and strife.

Like their fathers before them, Robert and Tommy's cultural background almost dictated which of the city's two giant clubs they would support. Allegiance to Rangers or Celtic carries a cultural significance above a mere love of the beautiful game for many nestled around the banks of the Clyde.

It is one of the ingredients that makes the meeting of these two teams, over 90 minutes of football, so special. Celtic versus Rangers is one of the fiercest rivalries in world football.

The CNN Belief Blog covers the faith angles of the day's biggest stories, from breaking news to politics to entertainment, fostering a global conversation about the role of religion and belief in readers' lives. It's edited by CNN's Daniel Burke with contributions from Eric Marrapodi and CNN's worldwide news gathering team.